In the manufacture of lead acid industrial and automotive storage batteries, it is customary to mold lead bushings in the plastic cover of the battery and to thereafter fuse the bushings to posts of the battery cell assemblies. Typically both the posts and bushings must be heated to temperatures above their melting points such that there is a fusion of the materials of the two components.
It has long been the practice to melt the ends of the posts and bushings by means of manually operated acetylene torches. Not only does such manual acetylene torch burning of the posts and bushings fail to lend itself to use in fully automated battery production lines, the quality and depth of the fused areas cannot be uniformly controlled. Moreover, particular care must be taken in not melting or otherwise damaging the portion of the plastic cover immediately adjacent the bushing, which can render the battery defective or sufficiently weaken the seal and support between the plastic cover and bushings as to create a potentially dangerous condition during use of the battery. Such acetylene torch burning, furthermore, is tedious and potentially harmful to the working environment, and it is difficult to control the flow of melted lead, resulting in unsightly irregularities in the surfaces of the finished battery terminals.
While various proposals have been made for automatically fusing battery terminal posts and cover bushings by means of acetylene torch heating, tungsten inert gas welding, electrical resistance heating, and electrical induction heating, such proposals all have faced various drawbacks, including the inability to obtain reliable fusion depths within the requisite processing time, undesirable melting of the cover about the bushings, unacceptable appearance of the finished terminals, or the necessity for utilizing auxiliary molds to control melted lead and achieve acceptable terminal appearance.